1. Field of the Invention
The present invention relates to a vertical cavity surface emitting laser diode (hereafter denoted as VCSEL).
2. Related Background Art
Nishiyama et al. has reported a VCSEL with a buried tunnel junction in “Electronics Letters, vol. 39(5), (2003) pages 437-439.” Their VCSEL provides, on the InP substrate, a semiconductor distributed Bragg reflector (hereafter denoted as DBR) made of a combination of AlGaInAs and InP, an active layer, an n-type InP layer to bury the tunnel junction, and a dielectric DBR made of a combination of amorphous silicon (a-Si) and aluminum oxide (Al2O3).
Because the tunnel junction buried by the n-InP layer has a mesa shape, the top of the n-InP layer inherently provides a step reflecting the mesa shape. The dielectric DBR surrounds this step and the dielectric DBR comprises a plurality of first films with relatively smaller refractive index and a plurality of second films with relatively larger refractive index alternately stacked to each other. Moreover, the second film with smaller refractive index comes in contact with the top of the semiconductor; accordingly, the interface between the semiconductor, whose refractive index is generally higher than that of the second film, and the first film causes a large difference in the refractive index, which enhances the scattering of the light thereat. Because the dielectric film directly coming in contact with the semiconductor is the first film with relatively smaller refractive index, the anti-node of the optical standing wave positions at the interface. Accordingly, the scattering of the light at the interface becomes relatively enhanced.